Most modern internal combustion engines utilize a form of electronic fuel-injection (EFI) system to control the air/fuel ratio (AFR) of the combustion mixture. The EFI system works to control the air/fuel ratio under all operating conditions to achieve the desired engine performance, emissions, driveability, and fuel economy. EFI systems use a programmed electronic control unit (ECU) or module (ECM) to monitor engine operating conditions and control fuel injection to increase or decrease the air/fuel ratio depending on the engine operating conditions. The ECU operates either in an open-loop controlled fuel injection with predetermined fuel maps, or in a closed-loop feedback-controlled fuel injection. Closed-loop feedback-controlled fuel injection varies the fuel injector output according to real-time sensor data rather than operating with the predetermined (open-loop) fuel map. Real-time sensor data from an oxygen sensor (or “O2 sensor”) is used to measure the proportion of oxygen (O2) in the exhaust gas. The oxygen sensor generates an electrical voltage indicating the amount of oxygen measured in the exhaust gas. The oxygen sensor generates a voltage in the range of about 0 to 1 volts. Higher voltages (greater than 0.5 volts) means there is less oxygen in the exhaust and indicates a rich mixture. Lower voltages (less than 0.5 volts) means there is more oxygen in the exhaust and indicates a lean mixture. The ECU reads the oxygen sensor voltage signal and produces fuel injector control signals to operate the fuel injectors to either richen the fuel mixture or to lean the fuel mixture.
For gasoline fuel burning engines, manufactures typically preprogram the ECU to control the fuel injectors to maintain a stoichiometric AFR of 14.7:1 for the majority of engine operating conditions. Any mixture less than 14.7:1 is considered to be a rich mixture, any more than 14.7:1 is a lean mixture. Most oxygen sensors are manufactured to generate a voltage of 0.5 volts when the AFR is 14.7:1.
It is known to modify an existing ECU to adjust the performance of the internal combustion engine. Heretofore, modifying an existing ECU has required reprogramming the programmable eprom or computer chip, replacing the eprom with another eprom having a different program, or piggy backing the ECU with another controller that operates to intercept signals, modify the intercepted signals and then pass the modified signal to various engine operating components to achieve the desired engine performance.
Various problems can arise when an existing ECU is modified as indicated above. The physically changed or new eprom must be to manufacture's application, and during use may cause knocking, drivability issues both at idle and wide open throttle, lean misfires, detonation, signaling of trouble codes in vehicles equipped with on-board diagnostic (OBD), void manufacture's warranties, and require physical modification of the engine's electrical wiring harness.
Accordingly, there is a need for an apparatus and method that can be employed to modify the performance of internal combustion, and specifically, the air/fuel ratio of an internal combustion engine that overcomes the drawbacks of the prior art.